def classify(number):
    """ A perfect number equals the sum of its positive divisors.

    :param number: int a positive integer
    :return: str the classification of the input integer
    """
    if type(number) != int or number <= 0:
        raise ValueError("Classification is only possible for positive integers.")
    aliquot_sum = 0
    for i in range(number-1):
        if number % (i+1) == 0:
            aliquot_sum += (i+1)
    if aliquot_sum == number:
        return 'perfect'
    if aliquot_sum > number:
        return 'abundant'
    else:
        return 'deficient'
